This review was published on December 21, 2007. Since then, this product may have been discontinued or replaced. Pricing and availability may differ from what is stated in the review.

Testing/Performance

Color*(10.19)

*During the past year, Canon’s point-and-shoots and DSLRs have performed exceptionally well in our color accuracy test. Like other high-end Canon cameras, the 40D has a Picture Style menu, with options that each handle color differently. Options include Standard, Faithful, and Landscape. Two Picture Styles that have a large impact on color accuracy are Standard and Faithful. Standard saturates colors, making them look vibrant but slightly unnatural. Faithful aims to keep colors as accurate as possible so users can enhance them as they wish during post-processing.

To test the color accuracy of the 40D, we set the camera to Faithful and photographed an industry standard GretagMacbeth ColorChecker test chart. The ColorChecker chart consists of 24 color tiles that represent colors from around the color spectrum. We determine color accuracy by comparing the colors the camera reproduces with the known colors of the test chart. The image below shows these colors side by side. The outside squares show the colors the camera reproduces, the inside squares show the ideal colors of the chart corrected for luminance, and the inner rectangles are the ideal chart colors at a perfectly even exposure.

Comparing the outer squares with the inner squares, you can see how many of the tiles match up well. There is, however, some differences in the color tiles in the third row, which represent very saturated colors. The 40D's colors look slightly undersaturated compared to the ideal chart colors. The graph below shows the color error in a more quantitative way. The ideal colors of the ColorChecker are shown on the color spectrum as squares, while the colors the 40D reproduces are shown as circles. The lines connecting the squares and circles show the magnitude of the color error for each color tile.

The graph confirms that many of the chart colors are accurate, except for a couple of the yellow and blue tiles. The 40D slightly undersaturates these colors, which is a bit disappointing considering 'Faithful' mode should be representing the colors as accurately as possible. Yet overall, this issue is nitpicky; the 40D's color accuracy is excellent, and the variety of shooting modes gives users many options to customize their color preferences. Canon cameras, DSLRs and point-and-shoots both, have shown tremendous color accuracy throughout the past year, a trend we hope to see continue.

**Resolution ***(8.76)

*With 10 megapixels on its CMOS sensor, the 40D offers more resolution than its predecessor, the 8-megapixel 30D. We test resolution by photographing an industry standard resolution test chart at varied focal lengths, apertures, and shutter speeds. We then run the images through Imatest to determine the sharpness of the camera and the settings that produce the sharpest image. Imatest measures resolution in terms of line widths per pixel height (lw/ph), which represent the number of equally spaced black and white lines that can fit across the image frame before becoming blurred. Imatest also analyzes the amount of sharpening (or lack of sharpening) applied to images by the camera. Too much sharpening can destroy image information and lead to image artifacting, but too little sharpening requires significant post-processing.We tested the 40D’s resolution using a Canon EF 24-70mm f/2.8L lens.

The 40D proved to be sharpest in Standard mode at ISO 100, f/11.0, and a focal length of 42mm. The camera resolved 1710 lw/ph horizontally with 1.9 percent undersharpening, and 1782 lw/ph vertically with 5.0 percent undersharpening. These amounts of sharpening are ideal because they provide sharp images without destroying information. Shots taken at shorter focal lengths tend to have great sharpening levels, but shots taken at longer focal lengths were much more undersharpened. In Neutral mode, the images were undersharpened as much as 35 percent. This mode is designed with post-processing in mind. The overall resolution, however, was good but not great. The camera actually scored slightly lower than the 30D, as well as below most other comparable DSLRs on the market, such as the Nikon D200 and D80, and the Canon 5D. Overall, the resolution is rather disappointing, though it should still allow for fairly large printing.

**Noise – Manual ISO ***(11.10) *

All electronic devices are subject to signal noise, whether it’s static in TVs, background hiss in stereos, or image noise in digital cameras. Image noise in photographs often takes the form of sandy graininess or small colored splotches that look unpleasant and hide fine image detail. From an engineering perspective, noise is increased when more megapixels are added to a sensor. This is because the pixels must be smaller to fit on a sensor of the same size. Smaller pixels capture less light, and thus have a worse signal-to-noise ratio than bigger pixels. The engineering challenge in keeping noise levels low is to decrease the amount of noise created in each pixel, or to use the image processor to smooth over or subtract noise after a photo is taken. The latter choice, however, can lead to degradation of image sharpness and detail. The 40D has an option to apply noise smoothing, called High ISO Speed noise reduction, which can be found in the Custom II menu.

We evaluate noise performance and characteristics by photographing a test chart under bright studio lights at every ISO setting, with the High ISO noise reduction set to both on and off. We run the photos through Imatest, which measures noise levels in terms of the percentage of image detail the noise drowns out.

The 40D’s 10-megapixel 22.2 x 14.8mm CMOS sensor keeps noise levels impressively low throughout the ISO range. Noise levels are extremely low at ISO 100, and increase slowly and steadily up to ISO 1600, where noise levels are still low. Closer examination of the noise characteristics show the noise to be fine-grained, slightly colored splotches. With noise reduction turned on, the color in the noise is mostly removed, with very little loss of detail. The only perplexing aspect of this impressive noise reduction is that, as the graph shows, it not only reduces noise in High ISO shots, as stated, but in shots taken at all ISO sensitivities. As impressive as the low noise levels are in the 40D, however, they do not quite reach the performance of the pro-level EOS 1D Mark III.

**Noise – Auto ISO ***(5.28)*

Under the same bright studio lights, we shoot our test chart with cameras set to Auto ISO to see how they handle noise. The 40D automatically shot at ISO 400, a rather high ISO speed for such bright lighting, but still kept noise levels nice and low. This is good news for users who like to keep settings on auto.

**White Balance ***(8.39)

*Accurate white balance is essential for producing accurate colors. Each kind of lighting source has a different color cast to it, and a camera must be able to adjust appropriately to each. We test white balance accuracy by photographing the ColorChecker test chart under four types of lighting: flash, fluorescent, outdoor shade, and tungsten. We shoot the chart using Auto white balance and the appropriate white balance preset. We have noticed an interesting trend over the past year or so; white balance accuracy in DSLRs is often worse than in point-and-shoots.

Auto (8.77)

Fortunately, the 40D has managed to buck this trend, though not in every respect. Set to Auto white balance, the camera is extremely accurate using its flash, solidly accurate under fluorescent light, but poor in outdoor shade and tungsten. As is usually the case, manually white balancing or shooting in RAW and white balancing on your computer will be much more accurate than using the Auto or preset settings.

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Auto WB - Flash Illumination

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Auto WB - Fluorescent Illumination

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Auto WB - Shade Illumination

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Auto WB - Tungsten Illumination

*Preset (8.00)

*Using the appropriate white balance presets, the 40D is very accurate with its flash. It performs poorly under fluorescent and outdoor shade, but well under tungsten. Always use the tungsten preset when shooting under tungsten lights unless you like the extremely yellow cast your images will take.

In addition to our bright light color and noise tests described above, we test cameras in less-than-ideal light conditions. To test color and noise accuracy in low light, we photograph the ColorChecker at light levels of 60, 30, 15, and 5 lux. Sixty lux corresponds to the amount of light in a room softly lit by two lamps, 30 lux is equal to a room lit by a single 40-watt bulb, 15 lux is similar to a room lit by a television, and 5 lux is about as bright as standing in a closet with the glow of an MP3 player. All shots are taken at ISO 1600, with High ISO speed noise reduction on and off.

We also test long exposure performance by shooting the ColorChecker at different shutter speeds, from 1 to 30 seconds. We take these shots at ISO 400 with Long Exposure noise reduction on and off. In long exposures, noise stays impressively low, and color accuracy is maintained fairly well. The Long Exposure noise reduction appears to have almost no effect on the noise levels, nor does it show a visible difference in the images.

**Dynamic Range ***(10.09) *

Dynamic range is an important image quality factor that describes the range of tones a camera can discern. A camera with good dynamic range will not blow out highlights and lose image detail in dark areas of the same photo. This is especially important for wedding photography (white dress and black tux), and nature or architectural photography in direct sunlight (bright highlights and dark shadows). We test dynamic range by photographing a backlit Stouffer test chart, which consists of a long row of rectangles, each a slightly darker shade of gray, ranging from brightest white to darkest black. The more rectangles a camera can distinguish, the better its dynamic range.

The 40D’s dynamic range at ISO 100 is excellent, and falls off slowly up to ISO 1600. Keeping the camera at as low an ISO setting as possible always yields the best dynamic range, but anything up to ISO 400 on the 40D is fantastic. It doesn’t fall off too badly at higher ISO speeds, either. Overall, the 40D edges out its predecessor, the 30D, and comes impressively close to the 1D Mark III. This is an excellent camera for wedding photography, either on its own or as a backup to a pro model.

Before you buy the Canon EOS 40D, take a look at these other cameras.

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